This action allows you to select your Registration Template from the list of all of your templates, and generates a new random discount code that people can use when registering for an event using that template. You can use text or an attribute to determine the code length (minimum length of 3 digits), the amount (in percent or real value), how many times the code can be used (useful for "the first 100 registrants get a discount" type scenarios), the maximum and minimum number of registrants that the discount should apply to, and the date range in which the code is valid. It will store the resulting code in the Text type attribute you select in the last box.

Takes an existing registration code (as text) and updates the amount of the discount that it gives. You can optionally have this affect past registrations which used that discount code, in addition to new registrations.
Additional Details

Be careful using the "Update Past Registrations" option- remember that people will have been told the total amounts that is due (and received a confirmation email proving it), and that if you set this to "Yes", that you're changing that amount on them in mid-stream and with no (automatic) notice. Personal contact is going to be key, if you find you have to do this.